Grid leak



June 15 1926.

Q. A. BRACKETT GRID LEAK Filed Sept. 29 1921 l WITNESSES: INVENTOR Patented June 15, 1926.

UNITED STATES PATENT OFFICE.

QUIliTCY BRACKETT, OF SPRINGFIELD, MASSACHUSETTS, ASSIGIN'OR ,TO WESTING- COMPANY, A CORPORATION OF PENNSYL- HOUSE ELECTRIC & MANUFACTURING VANIA. a

emu LEAK.

Application filed September 29, 1921. Serial No. 504,126.

My invention relates to wireless telegraphy and more especially to grid leaks which are employed in connection with electron' tubes.

The object of my invention is to provide a vacuum-tube device embodying means 'for adjusting the rate of leakage of the charge which accumulates on the grid of such devices. q

In the operation of three-electrode; tubes as detectors or as" oscillation generators, it is desirable to control the rate of leakage of the negative charge which builds up on the grids of the tubes during normal operation.

Heretofore, it has been customary to determine the. rate of leakage of the charge'by shunting the grid, and the filament of the tube with a resistor of relatively high value. Such resistors have taken the form of carbon impregnated paper or of metallic particles held together by means of vitreous material. A disadvantage in the use of resistors of such types, however,-is the difficulty of obtaining, in quantity production, resistors having similar characteristics: For example, resistors constructed under, like conditions have been found to vary in effective value by many thousands of ohms. Furthermore, such grid-leak devices, as have been brought to my attention, have been found subject to the phenomenon. of ageing, that is' to say, their effective value has chan-ged\ materially with time, and they "are likewiseseriously affected by atmospheric chan es.

According to my invention, I provi e, in the ordinary three-electrodetube, an auxiliary hot cathode which may be caused to control the rate of leakage of the charge from the grid of the tube. The auxiliary hot cathode is electrically connected to the grid of the three-electrode tube and is so disposed that the main hot cathode of the tube serves as an anode for said auxiliary hot cathode when the grid assumes anegative charge. By adjusting the temperature of said auxiliary hot' cathode, the rate'of leakage of the charge from the grid may readily be controlled- Other objects of my invention, as well as details. of construction, whereby my inven- 'sion system.

tion may be practiced, will be apparent from the following description referring to the accompanying drawing, wherein;

- Figure 1 is a diagrammatic view of an electron tube'embodying my invention, as

applied to a wireless receiving system; and Fig. 2 is a similar View, but showing my, invention as applied to a wireless transmis- Referring toFig. 1, I have shown an antenna 1 connected to; a ground 2 through aprimary winding 3 of a coupling transformer A secondary winding-5 (of the coupling transformer 4 has its opposite terminals shunted b a condenser 6 to form a resonant circuit and is connected by conductors ,8 and 9 tea grid'll and to a hot cathode ,12, respectively, of a thermionic device 13. The conductor 8 has included in circuit therewith a .condenser 14 for causing the grid 11 to assume a negative poten tial upon the receipt of signal impulses in the antenna 1. V I

The thermionic; device 13 comprises a customary anode 15,. the grid 11, the hot cathode 12, which is energized from a source of energy 16,"and, in'additlon, a second hot "cathode 17 which is energized by means of a source ofenergy 18 through a variableresistor 19. The auxiliary hot cathode 17 is connected to the grid 11 by means of a conductor 20 through a radio-fr'c quency choke coil 21. While the cathode 17 is shown as disposed immediately adjacent to themain hot cathode 12, it is not to be limited to such position. Upon the grid '11 assuming a negative potential, the main hot cathode 12 I serves'an an anode for the auxiliary electron-emitting cathode-17. A plate-filament I circuit comprises an indicating device 22 and a source of'energy 23.

In. Fig. 2, the thermionic device 13 is connected in a well known oscillation gene-- rator system. A plate-filament circuit includes a portion 24 of a tuning coil 25 and a ,variablecondenser 26, and may be energized by means of, a source of direct-current" energy 27. which,is connected to opposite terminals of the condenser 26 through reactors '28 and29. I I

' A grid-filament circuit includes a condenser 31 for causing the grid 11 to assume a negative potential and a feed-back coil 32 which is inductively related to a portion of the coupling coil 25. The auxiliary cathode 17 has been shown disposed within the tube 13, similarly to that shown in Fig. 1, and is energized from a source of energy 32 through a resistor 33 and a pair of radiofrequency choke coils 34, 35. The filament 12 may be energized from a. source of energy 36 through a resistor 37 .7 A conductor 35 serves to connect the grid 11 and the auxiliary filament 17.

In order to simplify the drawing in so far as ppssible, I have omitted means for control 'ng the transmission of the radio-frequency energy which is generated by the system. As will be readily understood by those skilled in the art, however, any of the well. known systems of modulation may be employed.

In operation, referring to Fig. 1, during the receipt of incoming m'gnal impulses, such, for'example, as those radiated from a spark transmitter, each wave train thereof tends to cause the grid 11 to assume a negative potential. In order that each wave train may produce a maximum change in the current traversing the plate-filament circuit of the tube, that is, maximum effect on the indicating device 22, it is necessary that the negative charge be dissipated between successive incoming wave trains. In my invention, the desired result just mentioned is readily effected by adjusting the temperature of the auxiliary hot cathode 17 through the variable resistor 19 to an optimum value giving the largest current variations in the plate-filament circuit of the tube.

Referring to Fig. 2 upon adjusting the constants of the platelament and the gridfilament circuits to their proper value, radio-frequency currents are generated by the tube in accordance with well known theories. In 'this application, the rate of leakage of the negatve charges, which are built ,up on the grid by reason of the condenser 31, may again be readily controlled lliy varying the temperature of the cathode While I have described only two modifications of my invention, it will be obvious to those skilled in the art that itis susceptible of many minor changes, alterations and modifications without departing from the spirit thereof. I desire, therefore, that only such limitations shall be imposed thereon as are indicated by the prior art or are specifically set forth in the appended claims.

I claim as my invention:

1. In an evacuated electric device, an anode, an electron-emitting cathode, a grid electrode, a second electron-emitting cathode and means for maintaining said last-mentioned cathode at grid potential, whereby said cathodes serve as electrodes for providvcomprising an anode, a cathode, a grid and a second cathode immediately adjacent to said first-mentioned cathode, a conductor connecting said grid and said second cathode, means associated with said electrodes for causing said grid to assume a negative po tential, means associating said second cathode with said grid to cause the space be tween said cathodes'to constitute a grid leak, and means associated with said second. cathode for adjustin the rate of leakage of the charge from sai grid.

4:- In a wireless system, an electron tube comprising an anode, a cathode, a grid and a second cathode immediately adjacent to said first-mentioned cathode, a conductor connecting said grid and said second cathode, means associated with said electron tubefor causing saidgrid to accumulate a negative charge, means associating said second cathode with said grid to cause the space between said cathodes to constitute a grid leak, and means for adjusting the temperature of said second cathode, whereby the rate of leakage of the charge from said grid may be selectively controlled.

5. In a wireless system, an electron tube I comprising an anode, a cathode, a grid and a second cathode immediately adjacent to said first-mentioned cathode, a conductor connecting said grid and said second cathode, a circuit connecting said grid and said first-mentioned cathode and embodying a source of energization and a series connected condenser, and means for adjusting the temperature of said second cathode, whereby the impedance of the space-current path between said cathodes may be controlled to correspondingly vary the rate of leakage of a charge from said grid.

' 6. The combination with an evacuated electric device having two electron-emitting electrodes and an anode, of means for establishing a space-current flow between one ofsaid electrodes and said' anode, a grid circuit for iac electrodes in a grid-leak path shunting said condenser. 1

7; A vacuum-tube oscillation-generator of the feed-back typeincluding a vacuum tube having two electron emitting electrodes and an anode, means for establishing a spacecurrent flow between one of said electrodes and said anode, a grid circuit for controlling said space-current flow, a grid condenser included in said circuit and connections for including said electron-emittin electrodes in a id-leak path shunting sai condenser.

11 testimony whereof, I have hereunto subscribed my name this twenty-sixth day of August 1921.

QUINCY A. BRACKETT.' 

